A. Field of Invention
This invention pertains to an apparatus for precise and repeatable translation of objects along a track. In a particularly advantageous embodiment of the invention, two substantial assemblies are combined within an apparatus for positioning an object accurately and repeatedly along two orthogonal axes.
B. Description of the Prior Art
In the modern age of automation in production and inspection processes, it is often required to position an object in two orthogonal coordinates, such as XY or XZ coordinates. Usually, this is accomplished by stacking two one-axis positioners on top of each other, so that the top positioner is perpendicular to the bottom one. For example, a dual axis Model MT160 stage is constructed by mounting one stage on top of the other as shown on page 56 in catalog 588 by Klinger Scientific, 999 Stewart Avenue, Garden City, N.Y. 11530. The resulting assembly is very bulky. It is difficult to provide precise orthogonality of two positioners. The weight of the top positioner is loading the bearing system of the bottom positioner. Furthermore, such an assembly can not be used in applications. where an object, positioned in two coordinates, must be transparent, for example, for a light source in the inspection process.
So-called open frame tables are designed for applications which require a large center opening through which light can pass or objects can be mounted. For dual axis positioning, open frame tables are also mounted on top of each other. Such an assembly is shown on page 88 in the 1989-1990 catalog "Positioning Systems and Components" by Daedal, Box 500, Harrison City, Pa. 15636. It is obvious that both openings are aligned only in a stationary position. When an object mounted on the upper open frame is positioned in two coordinates, there is always a moving dead zone for passing light, wherever the bottom frame interferes with the opening in the upper frame.
So-called Gantry type XY positioners are assembled from three one-axis positioners. For example, a model GV 88 XY is shown on page 65 in catalog 588 by Klinger Scientific. A single X axis slide is supported and translated by two Y axis slides. Such an assembly is complicated and therefore expensive and very sensitive to an alignment of both Y slides. Other manufacturers control each Y positioner by a separate motor and have problems in synchronizing those motions.
Therefore, there is a need for integral, low profile, inexpensive XY positioners, suitable for applications where an object positioned in two coordinates is transparent for a light or optical beam without a dead zone.